英語聽力文摘 老忠實(shí)噴泉

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老忠實(shí)噴泉是美國黃石公園中最負(fù)盛名的景觀。黃石最著名的間歇泉是老忠實(shí)噴泉，它不像其他噴泉那樣爆發(fā)沒有規(guī)律，它每隔幾十分鐘,就會噴發(fā)一次,從不叫旅客失望。它始終如一的忠實(shí)受到世人的喜愛。老忠實(shí)噴泉每隔56分鐘噴出一次，每次歷時約4分鐘，噴得最高最美之時是前20秒，每次共噴出熱水約1萬加侖，高度達(dá)40-50米，水溫攝氏93度。經(jīng)冬歷夏，老忠實(shí)噴泉都這樣按照一定的規(guī)律不竭地噴著，遂得“老忠實(shí)”這樣的美名。人們來到黃石公園，必到老忠實(shí)噴泉一睹為快。但見它不噴則已，一噴則如萬馬奔騰，更兼在陽光輝映下，水蒸氣閃出七彩顏色，蔚為壯觀，誰人能不發(fā)出贊嘆之聲。

In Yellowstone National Park you can visit the geyser Old Faithful.

It’s a spectacular sight, as each four-minute-long eruption sends boiling water over a hundred and fifty feet high. On today’s Moment of Science, we’ll learn how a geyser works.

Geysers spout up where a column of underground water is heated to boiling by “magma,” or molten rock. Like a pan boiling over on your kitchen stove, this boiling pushes the water upward.

Old Faithful got its name because it used to erupt– faithfully–every sixty-five minutes. It’s been more irregular since a 1959 earthquake disrupted its natural, underground plumbing.

If Old Faithful were exactly like a pan on a stove, you’d expect the water to bubble out continually. What makes it alternate between quiet dormancy and exploding action?

This has to do with the way a deep column of water boils. Water’s boiling point is depending on its pressure. At sea level, water boils at 212°F. Deep under Old Faithful, where the molten rock is, the pressure is much greater. Water won’t boil here until it’s over 300°.

What happens is this: The water column gradually heats, but high pressure keeps the deeper parts from boiling. Finally, the column gets hot enough for the top part to boil off. As the top turns to steam, this reduces the pressure on the deeper water–and lowers its boiling point!

Remember, this deep water is already quite hot. Reducing the pressure makes it boil immediately, further reducing pressure for even deeper water. It’s a rapid chain reaction that makes the whole column boil at once, erupting a spout high into the air. After each eruption, the column refills with cool water from an underground source, and the whole cycle begins again.

譯文：

在黃石國家公園，你可以參觀老忠實(shí)噴泉。每四分鐘泉里都會噴出高一百五十英尺的沸水，這可真是一幅壯麗的景色。在今天的科學(xué)一刻中，我們將要學(xué)習(xí)噴泉是如何工作的。地下水柱受到沸騰的“巖漿”(即融化了的巖石)加熱便會噴出地表，形成噴泉。就像廚房爐子上煮沸的鍋，沸騰加熱使水上升。

老忠實(shí)泉曾經(jīng)非常守信地每六十五分鐘噴發(fā)一次，由此而得名。自從1959年地震破壞了它天然的地下管道以后，老忠實(shí)泉就變得更加不規(guī)律了。

如果老忠實(shí)泉就像在爐子上的鍋一樣，水會持續(xù)不停地沸騰外冒。那么，到底是什么讓它一會兒靜如冬眠的小獸，一會兒又噴薄不止?

這與底層水柱的沸騰方式有關(guān)。水的沸點(diǎn)取決于氣壓。在海平面上，水達(dá)到華氏212度就會沸騰。在老忠實(shí)泉的深處，熔巖活動的地方，氣壓要高得多。在這里，水要達(dá)到華氏300度才會沸騰。

于是就有了這樣的情況，水柱逐漸加熱，但是高壓使更深層的水無法沸騰。最后，水柱達(dá)到足夠的熱量使頂部的水汽化。當(dāng)頂部的水變成蒸汽后，就減少了對深層水的壓力-并降低其沸點(diǎn)。

需要明確的是，此時底層的水已經(jīng)很熱了。氣壓的降低讓其迅速沸騰，這樣以此類推又緊接著降低更深層的水的壓力。這是一個讓整個水柱立即沸騰的快速連鎖反應(yīng)，水柱噴薄而出。在每次噴發(fā)之后，地下的冷水重新填滿水柱，沉靜噴發(fā)的循環(huán)又開始啦!